The invention relates to a method of marking or inscribing surfaces, more particularly surfaces of metals.
With metals there are a variety of marking methods known. For example a marking may be produced by means of application of material, such as with ink, or else with depletion of material, such as in the case of engraving.
It is also possible to perform what is referred to as temper marking or else oxidation marking. This means that the metal at its surface undergoes changes in color in certain areas as a result of selective temperature change. In the case of metals which are heated to a predeterminable temperature, oxidation processes on the surface give the surface a colored appearance and hence a colored coloration, inscription or marking. In this case it is possible to influence the thickness of the oxidation layer, since the diffusion of the oxygen atoms is dependent on the tempering temperature and/or the tempering time.
For example, different oxide layers on the surface exhibit an iridescent chromatic coloration of the surface. This color effect is used in stainless steel in accordance with the prior art, since at around 500° C. a dark-gray to black temper color is formed.
In order to carry out marking, lasers are used to produce a temper mark. In this operation, when the laser light is employed on the direct surface of the metal, there is a disadvantageous surface effect, since the laser light is coupled in directly on the surface and as a consequence in the zone of heat influence, there are burrs, furrows, melting events and metallurgical changes in microstructure. A surface layer is consequently roughened and/or its microstructure altered, and so, for example, there may even be instances of weakening of the material. This may be disadvantageous in particular in the case of certain fields of application, as for example in medical engineering or else in other fields of application where the desire is for particularly smooth or clean marked surfaces.